Chem 30A

Ch 5. Molecules and Compounds Chemical Formulas of Compounds 1. A given compound always has the same numbers and types of atoms (constant composion). 2. Each atom is represented by its element symbol. 3. The number of each type of atom is indicated by a subscript to the right of the element symbol (Excepon: If just one atom, no subscript). 4. Typically, the more metallic element is listed first.

Ex Probs Molecular Compounds and Ionic Compounds Types of Compounds

Molecular Compounds Ionic Compounds • Covalent bond • Ionic bond

• One unit: Molecule • One unit: Formula unit

O

H H + – Chemical Bond

Chemical bond: A force that holds groups of atoms together and makes them funcon as a unit.

• Bonding involves just the electrons of atoms! Molecular (Covalent) Compounds • Held together through Covalent Bonds: Bonds in which electrons are shared between the bonded atoms.

H H H2

• Molecule: a group of two or more atoms which are covalently bonded (a unit of molecular compound) • Nonmetal + Nonmetal à Molecular Compound

Molecules

H H O

H H Cl Cl C C O H H O

Compounds Elements

• Note: Both compounds (eg, H2O) and elements (eg. O2, H2) may exist as molecules. Representing Molecules

CH4 Chemical formula

H Ball-and-sck model

H C H

H

Structural formula Space-filling model Ionic Compounds • Held together through Ionic Bonds: Bonds in which oppositely-charged ions are held together by electrostac aracon between them.

+ –

• Formula unit: A group of two or more ions which are bound through ionic bonds (a unit of ionic compound) • Metal + Nonmetal à Ionic Compound

Formula Units • Formula units exist as a part of a larger 3D array (a solid). Ionic Compounds • Most commonly, ionic compounds form when metals combine with nonmetals à Metal element transfers electrons to the nonmetal element.

Metal caon + Nonmetal anion à ionic compound Isolated ions don’t exist! Formation of an Ionic Compound Overview: Fundamental Components of Matter Matter

Pure Substances • Elements • Compounds

“Parcles” of Maer • Atoms • Ions • Molecules

Elements, Compounds, Atoms, Molecules, Ions

Elements Compounds (1 type of atom) (more than 1 type of atom)

• + – Atomic • Ionic

• Molecular • Molecular Elements, Compounds, Atoms, Molecules, Ions

Ex Probs Formula (Molecular) Mass Formula (Molecular) Masses of Compounds

Formula mass of a compound = sum of atomic masses

eg. Molecular mass of H2O = 2(atomic mass of H) + 1(atomic mass of O) = 2(1.008 amu) + 1(16.00 amu) = 18.02 amu

Ex Probs Chemical Nomenclature Chemical Nomenclature • Chemical Nomenclature: a system of naming chemical substances

Common Name Systemac Name Formula

Grain alcohol Ethyl alcohol CH3OH

Rubbing alcohol Isopropyl alcohol C2H5OH

Laughing gas Dinitrogen oxide N2O

Milk of Magnesium Mg(OH)2 magnesia hydroxide

Epsom salt Magnesium MgSO4Ÿ7H2O sulfate heptahydrate Chemical Nomenclature

A. Ionic Compounds (Binary and Polyatomic) B. Covalent Compounds (Binary) C. Acids

Formulas (NaCl) Names (sodium chloride)

Refer to Chemical Nomenclature Handout for rules for naming and wring formulas.

Naming Compounds Naming Binary Ionic Compounds

• The caon is always named first and the anion second. • Remember: Ionic compound has a net charge of 0. • METAL + NONMETAL = ionic compound

Naming Binary Ionic Compounds: Fixed Charge Caon Ionic compounds containing fixed-charge metals (mostly main group metals): 1. A monatomic caon has the same name as that of the parent element. 2. A monatomic anion is named by taking the root of the element name and adding –ide.

• Examples KCl potassium chloride

MgBr2 magnesium bromide CaO calcium oxide Ex Probs Naming Binary Ionic Compounds: Variable Charge Cations

Ionic compounds containing variable-charge caons (mostly transion metals): For metals that can form caons of more than one charge, the charge on the metal ion must be specified with Roman numeral in parentheses!

• Examples CuBr Copper(I) bromide FeS Iron(II) sulfide

PbO2 Lead(IV) oxide

Common Ion Charges (Memorize!)

Metals form caons. Nonmetals form anions. • Groups 1A,2A,3A: • Group 5A: charge = -3 • Group 6A: charge = -2 charge = group # • Group 7A (halogens): • Transions metals: charge = -1 Many have variable • Group 8A (noble gases): charges. charge =0 Ex Probs

Naming Ionic Compounds with Polyatomic Ions

Ions can be simple (monatomic) or polyatomic. • Simple Ions: Mg2+, Li+, Cl-, O2-

• Polyatomic Ions: + - NH4 NO3

N N

+ - NH4 NO3 Naming Ionic Compounds with Polyatomic Ions

Names and charges of polyatomic ions must be memorized. (Memorize the following!)

• Polyatomic caons: Names end in -ium. + + NH4 = ammonium H3O = hydronium

• Polyatomic anions: Many contain oxygen. – 2– OH = hydroxide CO3 = carbonate – 3– NO3 = nitrate PO4 = phosphate 2– – SO4 = sulfate CN = cyanide

Common Polyatomic Ions Naming Ionic Compounds with Polyatomic Ions

Examples of ionic compounds with polyatomic ions

• NH4Cl ammonium chloride

• Na2CO3 sodium carbonate

• Mn(OH)2 manganese (II) hydroxide

• (NH4)2SO4 ammonium sulfate

Ex Probs Naming Binary Molecular (Covalent) Compounds NONMETAL + NONMETAL Name first element first, second element second. 1. First element: Greek prefix + parent element (Excepon: Don’t use “mono-”). 2. Second element: Greek prefix + parent element + “-ide” (as if it were an anion). Naming Binary Covalent Compounds Examples of Binary Molecular Compounds

N2O5 dinitrogen pentoxide P4O6 tetraphosphorus hexoxide BF3 boron trifluoride NO nitrogen monoxide CO carbon monoxide

Ex probs Naming Problem

Which of the following compounds is/are named incorrectly?

a) KNO3 potassium nitrate b) TiO 2 tanium(II) oxide c) Sn(OH)4 n(IV) hydroxide d) PBr 5 phosphorus pentabromide e) CaCrO 4 calcium chromate Strategy for Naming Compounds

Look at the formula. Metal + Nonmetal Nonmetal + Nonmetal or Polyatomic Ions

MOLECULAR IONIC Compound Compound Name as Caon + Anion! Use Greek prefixes! (If see variable-charge caon, include charge in Roman numerals!) Ex probs

Writing Formulas Writing Chemical Formulas: Ionic Compounds

I. Ionic Compounds § Balance charges, since compounds must be neutral! Posive Charge + Negave Charge = 0

Examples

• magnesium bromide MgBr2 • iron(II) sulfide FeS

Ex probs Writing Chemical Formulas: Molecular Compounds

II. Binary Molecular Compounds § Greek prefixes indicate number of atoms. Greek Prefixes Examples mono one di two • dinitrogen pentoxide N2O5 tri three tetra four • boron trifluoride BF3 penta five hexa six

Ex probs Strategy for Writing Formulas of Compounds

Look at the name. Metal + Nonmetal Nonmetal + Nonmetal or See Greek prefixes Polyatomic Ions

COVALENT compound IONIC compound Follow Greek Balance charges! prefixes!

Ex probs Nomenclature for Acids Brief Intro to Acids and Bases Arrhenius Definion of Acids and Bases • Acid: a substance that makes proton (H+) in water. HCl à H+ + Cl- acid proton anion

• Base: a substance that makes hydroxides (OH–) in water. + – NaOH à Na + OH

Brief Intro to Acids and Bases Bronsted-Lowry Definion of Acids and Bases • Acids are proton (H+) donors. HCl à H+ + Cl- acid proton anion

• Bases are proton (H+) acceptors. + + NH3 + H à NH4 base proton caon

Strong and Weak Acids

• Strong acid: Completely ionized (dissociated). HCl(aq) H+(aq) + Cl-(aq)

• Weak acid: Most of the acid molecules remain intact. + - CH3COOH(aq) H (aq) + CH3COO (aq) equilibrium arrow

Naming Acids *Acids always have “H” first in their formulas! End all acid names with “acid.”

1. Binary Acids: Name format: “hydro-” + parent element

+ “-ic acid” Naming Acids

2. Acid with oxygen (Oxyacids):

Acid name is derived from oxoanion of that acid. • If anion ends in “ate” à acid name ends with “ic” acid. – § NO3 is nitrate à HNO3 is nitric acid • If anion of ends in “ite” à acid name ends with “ous” acid. – § NO2 is nitrite à HNO2 is nitrous acid Some Oxyacids Common Acids (Memorize!)

Strong Acids • HCl hydrochloric acid • HBr hydrobromic acid • HI hydroiodic acid

• HNO3 nitric acid • H2SO4 sulfuric acid • HClO4 perchloric acid

Weak Acid

• HC2H3O2 or CH3COOH acec acid • H2CO3 carbonic acid

Ex probs